Electromagnetic fluid mixture clutch



March 1955 w. P. LEAR ETAL ELECTROMAGNETIC FLUID MIXTURE CLUTCH FiledApril 12, 1950 pwzwroast- Wllliam E? Lear 6; Joseph 77?. Bosh/(a BY W 0iUnited States Patent ELECTROMAGNETIC FLUID MIXTURE CLUTCH William P.Lear, Santa Monica, Calif., andJoseph M.

Boshka, Holland, Mich, assiguors to Lear, Incorporated, Grand Rapids,Mich, a corporation of Illinois Application April 12, 1950, Serial No.155,468

7 Claims. (Cl. 192-215) So-called dry powdered iron electromagneticclutches relay for their action upon the interposition between thedriving and driven members of a mass of iron par ticles, e. g., terrumand carbonyl iron and the temporary unification of these members and theparticles through the medium of magnetic flux. dition of the clutch themass of particles lies idly in a cavity within the clutch, while uponenergization of the clutch coil practically all of the particles aredrawn into a desired orientation between the driven member, e. g.

a cup, and the pole pieces forming part of the driving 0 member. Thusthe driving member, driven member and the mass of particles, bonded bythe magnetic flux, revolve as a unit. Such clutches are characterized byhigh pullin and running torque, and, due to the absence of the largerubbing surfaces found in disc types of electromagnetic clutches, havelong life. it is possible to provide very little clearance between thedriving and driven members, hence a narrow gap and consequent highefficiency in the magnetic circuit.

By utilizing a cup rather than a disc for the driven member advantagemay be taken of the greater torque available at the larger diameter, andthis, together with the use of a narrow gap filled with the mass of ironparticles makes for a highly efficient mechanism capable of operation oncurrents on the order of a fraction of an ampere. Accordingly a clutchof this kind is ideally adapted for use with servo-mechanisms drivenfrom a push-pull amplifier of conventional design, e. g. automaticpilots for aircraft.

A principal object of the invention is to provide an improved form ofelectromagnetic clutch utilizing iron particles as the intermediary forengaging the clutch, and in which the actual zone of engagement isconstituted by a relatively narrow annular body of iron particlescoacting frictionally with similarly narrow pole pieces of the drivingmember and a correspondingly narrow region of the driven member, suchzone lying at a maximum peripheral position.

Another object lies in providing non-magnetic barriers at each side ofthe engaging zone further to concentrate the available flux.

A further object lies in forming one or both of the pole pieces in anovel manner to present a narrowed area of magnetizable material at theactual engaging zone.

Still another object is to provide a cup-shaped driven member which cupis cut out in a novel manner to permit rapid distribution of the ironparticles from idle condition to driving position upon energization ofthe clutch, and to reduce friction between the driving and drivenmembers and the particles during idling of the clutch.

Generally regarded, the instant improvements in one aspect involveforming the pole pieces of the driving member in their relation to thecup-shaped driven memln the disengaged conher in such fashion that ahighly concentrated flux field M 2,705,064 Patented Mar. 29, 1955 ice isformed, the iron particles then filling the gap between the driving anddriven members to provide a flux path of extremely low reluctance. Inanother aspect the invention contemplates the provision of non-magneticbarnets on either side of the poles to minimize to a considerable degreethe fringe flux. in still another aspect the invention includes a drivencup which has apertures for permitting rapid distribtution of the ironparticles to the zone of engagement. In another respect the inventioncontemplates a novel composition of particulate magnetizable materialand other ingredients in combination wtih the remaining elements of theclutch.

Referring to the drawing which depicts one form in which the inventionmay be embodied in practice:

Fig. l is a vertical medial cross section through the clutch of theinvention;

Fig. 2 is a right hand end elevational view thereof, but with the brushstructure omitted for clarity;

Fig. 3 is a half-cross-sectional view taken on the line 3-3 of Fig. 1;and

Fig. 4 is a cross-section taken on the line 4'4 of Fig. 3 showing thedriving cup.

Turning to the drawing, the invention clutch comprises a driving member10, a driven member 11 and a mass of magnetizable particles 12 forproviding driving engagement when subjected to a magnetic field. Drivingmember 10 is constituted by an annulus 15 of paramagnetic material, e.g. Armco iron, an inexpensive composition having high magneticpermeability and good machining qualities. Secured to the right end facethereof is a disc 16 of Bakelite or equivalent insulating materialhaving good mechanical strength, the junction being effected by dowelpins 17. Secured to both the anulus 15 and disc 16, by the same pins 17,is a ring gear 18 through which power is transmitted to the clutch by apinion carried on the shaft of a motor (not shown). As will becomeevident the driving member 10 has a greater mass, by far, than thedriven member 11, and it is therefore preferred that the part of greatermass be maintained in constant rotation to reduce inertia effects uponengagement. By providing a shoulder on the an nulus 15 and fitting arecess of the gear 18 snugly thereover adequate support is given thelatter. Moreover by interposing a narrowed peripheral portion of thedisc 16 between the gear and annulus the disc is properly carried andsupported with respect thereto.

Grooves 21-21 in the outer face of disc 16 are fitted with slip rings22-22 against which brushes 23-23 are adapted to bear, and by means ofwhich current may be brought to the slip rings and thence to the clutchenergizing coil to be described.

Supported by its right-hand end within the interior of the annulus 15 isthe generally cylindrical clutch core 27 of the cross section shown. Arecess 28 of generally trapezoidal cross-section carries the clutchenergizing winding or coil 31 of pan-cake form. Conductors 33-33 arepassed through a notch 34 and aperture 35 in the core 27, and connectthe ends of the winding 31 with the rings 2222.

The flat left-hand face 24) of the core 27 and the lefthand wall of therecess 28 between them define a somewhat conical portion forming theinner pole piece 30, and whereby the flux emanating from the coil 31 isconcentrated into a zone defined by the narrow peripheral face 37 ofpole piece 30, such flux path being indicated by arrows.

To provide a barrier at one side for the magnetic flux a non-magneticring 41, e. g. brass, is brazed or otherwise united to the inneradjacent sloping face of the recess 28. Ring 41 is so dimensioned as toprovide a tight fit against the inner surface 32 of the annulus 15, thusto support the core 27 at its inner end.

A reduced portion of the core 27 is fitted into an aperture 26 in thedisc 16 to provide additional support for the latter. For cooling theclutch a plurality of fins 43 may be provided at the right-hand end ofthe core 27.

At its left end the annulus 15 is provided with an inwardly extendingflange 46, the inner axially extending cylindrical face whereof,constituting the other pole piece, is substantially coextensive with.the face 37 of the pole piece 30. Acting as a magnetic barrier on theleft-hand surface of the pole piece 46 is a second non-magnetic ring 48brazed or otherwise united with the annulus 15. Thus the flux across thepole pieces 30 and 46 is substantially confined to the relatively narrowcylindrical faces thereof, and fringe flux accordingly reduced to anegligible minimum.

An end housing 51 is tightly fitted over the ring 48, and is secured inany convenient manner to the annulus 15, thereby to enclose the innerparts of the clutch and to define a cavity 52 for the clutch drivenmember and the particulate composition to be described. Housing 51 maybe provided with circumferential fins 49 to facilitate cooling.

Rotatably supported in ball bearings 53 and 54 mounted in the housing 51and core 27 respectively is a shaft 55, and keyed thereto is thecup-shaped driven member 57 comprising a disc portion 58 of non-magneticmaterial, e. g. brass, to which is brazed a paramagnetic ring 59. Thislatter is so proportioned as to lie in the gap defined by the polepieces 30 and 46.

Deposited in the cavity 52 is a mass of paramagnetic material,preferably comprised as follows:

By weight- 75% ferrum 25% carbonyl E iron to which is added by weight:

2% lubricating graphite /2 of 1% boron nitride and ball milled for 72hours with /1 steel balls to insure complete homogeneity. After beingmilled and until used the composition is stored in a dry place. Asufficient quantity of this composition is added to the clutch to fillcompletely the spaces intermediate the driving and driven clutchmembers. In the drawing such mass of material is indicated by stippling.It has been found advisable to run-in the clutch for a period of time,which has been found to cause a reduction in the original mass ofpowder, i. e. packing. Accordingly additional powder may be added tofill again the indicated spaces. Notwithstanding even further minorpacking during the life of the clutch the efliciency is not reduced,since there will be an ample supply of powder to insure that theexpected magnetic driving connection Will be achieved.

It will be noted from the drawing that the peripheral portion 40 of thedriven member 57 is of such cross section as to position the same asnearly as possible to the magnetic gap defined by the poles 30 and 46,and hence to provide a non-magnetic barrier radially inwardly and as acompanion to the barrier ring 48. However a sufiicient throat 50 must beprovided to permit proper distribution of the powder 12.

In order to reduce rubbing friction between the driven member and thepowder, it is preferred to provide the disc portion 58 of the drivenmember with apertures 61 of as large a size as possible consistant withmechanical strength of the driven member, thereby to reduce thesuperficial area of the member and therewith the undesirable friction;and to notch or cut-out the flange 59 thereof for the same purpose.Furthermore such foraminous configuration of the driven member providesa passage from one face to the other thereof, thereby permitting rapiddistribution of the magnetizable powder in the space beween the polepieces, and its rapid dissemination therefrom.

While it is believed that the operation of the clutch is more or lessapparent from the preceding description, it will be understood that theclutch driving member, being constantly rotating, will have its winding31 supplied with energizing current via the brushes 23-43 and slip rings2222. Accordingly a flow of energizing current will create aconcentrated magnetic field across the pole pieces 30 and 46. Thereupona quantity of the powder in greater concentration than the deenergizedstatus will be found in the gaps intermediate the pole pieces and theflange 59 to lock the driving and driven members together for jointrotation.

In effect the particles have been found to act more like a solid than acomminuted mass thereby to provide virtually a non-slipping transmissionof torque in the fully energized condition.

While we have shown a particular embodiment of our invention, it will beunderstood, of course, that we do not wish to be limited thereto, sincemany modifications may be made, and we therefore contemplate by theappended claims to cover any such modifications as fall within the truespirit and scope of our invention.

Having thus described our invention, what we claim and desire to secureby Letters Patent is:

1. An electromagnetic clutch comprising a rotatable driving memberincluding a pair of annular poles so disposed as to define an annulargap, electrical means carried by said member for providing magnetic fluxin said gap upon energization of the clutch, a rotatable driven memberincluding a paramagnetic annular part positionedin said gap and definingan outer annular gap and an inner annular gap, a casing carried by saiddriving member for enclosing said gap and driven member, a mass ofpulverulent paramagnetic material disposed in said casing the bulk ofwhich material is adapted upon energization of the clutch to take up aposition in said gaps for uniting said part and driving member for jointrotation, a non-magnetic annular element united with said driving memberand positioned on one side of said outer gap, a second non-magneticannular element united with said driving member and positioned on theopposite side of said outer gap and bridging across both said gaps, anda non-magnetic annular element united with said driven member andpositioned adjacent said inner gap on the same side thereof as saiddriven member.

2. An electromagnetic clutch comprising a rotatable drivingmemberincluding a pair of annular poles so disposed as to define anannular gap, electrical means carried by said member for providingmagnetic flux in said gap upon energization of the clutch, a rotatabledriven member including a paramagnetic annular part positioned in saidgap, a casing carried by said driving member for enclosing said gap anddriven member, a mass of pulverulent paramagnetic material disposed insaid casing the bulk of which material is adapted upon energization ofthe clutch to take up a position in the spaces defined by said annularpart and gap for uniting said part and driving member for jointrotation, a non-magnetic annular element united with said driving memberand positioned adjacent said gap at that side thereof opposite saiddriven member, said non-magnetic element being bridged across said gap,and a second non-magnetic annular element united with said driven memberand positioned on the same side of said gap as said driven member.

3. An electromagnetic clutch comprising a rotatable driving memberincluding a pair of annular poles so disposed as to define an annulargap, electrical means carried by said member for providing magnetic fluxin said gap upon energization of the clutch, a rotatable driven memberincluding a paramagnetic annular part positioned in said gap, a casingcarried by said driving member for enclosing said gap and driven member,a mass of pulverulent paramagnetic material disposed in said casing thebulk of which material is adapted upon energization of the clutch totake up a position in the spaces defined by said annular part and gapfor uniting said part and driving member for joint rotation, anonmagnetic annular element united with said driving member andpositioned adjacent said gap at that side thereof opposite said drivenmember, and a second non-magnetic annular element united with saiddriving member and positioned on the same side of said gap as saiddriven member.

4. An electromagnetic clutch comprising a rotatable driving memberincluding a pair of annular poles so disposed as to define an annularspace therebetween, the end faces of the poles being substantiallycoplanar, a rotatable driven member including an output shaft, a webportion extending radially from said shaft and a magnetic flange portiondisposedrin said space to define with said poles an inner annular gapand an outer annular gap, electrical means carried by said drivingmember for providing magnetic flux in said gaps, a casing carried bysaid driving member and surrounding said poles and driven member, a massof pulverulent magnetic material contained in said casing, a part ofsaid material being adapted, upon energization of said electrical means,to take up a position in said gaps to couple said driving and drivenmembers for joint rotation, a first non-magnetic ring united with theouter pole at the end face substantially thereof and having a facecoplanar with the inner axially-disposed face of said outer pole, asecond non-magnetic ring united with both said poles and bridging saidgaps and the end face of said flange portion, and a third non-magneticring united with said flange portion and positioned closely adjacent theouter end of the inner gap but sufficiently far to permit unimpededcirculation of the pulverulent material into and out of said inner gapupon energlzation and deenergization of said electrical means.

5. An electromagnetic clutch comprising a driving member of paramagneticmaterial, said member having an internal space, an energizing windingmounted in said space, slip ring and brush means operatively associatedwith said member for connecting said winding to an ex ternal currentsource, said member comprising a substan tially cylindrical inner partand an annular outer part, said inner part having a radially outwardlyextending pole piece including a face disposed substantially axially ofsaid member, said outer part having a radially inwardly extending polepiece including a face disposed substantially parallel to said firstface and defining therewith a magnetic gap, a driven member having aparamagnetic part positioned in said gap to define with said faces apair of annular spaces, a casing carried by said driving member andenclosing said driven member, and a mass of pulverulent paramagneticmaterial disposed in said casing the bulk of which material is adapted,upon energization of the clutch, to be positioned in said spaces tounite said driving and driven members for joint rotation, a nonmagneticelement in contact with said pole pieces on that side thereof oppositesaid driven member and bridging said gap, to confine said material tosaid spaces, and a second non-magnetic annular element juxtaposed to theouter face of said inwardly extending pole piece and continuing to saidgap.

6. An electromagnetic clutch comprising a driving member of paramagneticmaterial, said member having an internal space, an energizing windingmounted in said space, slip ring and brush means operatively associatedwith said member for connecting said winding to an external currentsource, said member comprising a substantially cylindrical inner partand an annular outer part, said inner part having a radially outwardlyextending pole piece including a face disposed substantially axially ofsaid member, said outer part having a radially inwardly extending polepiece including a face disposed substantially parallel to said firstface and defining therewith a magnetic gap, a driven member having aparamagnetic part positioned in said gap to define with said faces apair of annular spaces, a casing carried by said driving member andenclosing said driven member, and a mass of pulverulent paramagneticmaterial disposed in said casing the bulk of which material is adapted,upon energization of the clutch, to be positioned in said spaces tounite said driving and driven members for joint rotation,

a non-magnetic element in contact with said pole pieces on that sidethereof opposite said driven member and bridging said gap, to confinesaid material to said spaces, and said driven member being providedwitha non-magnetic annular part disposed contiguous to said gap.

7. An electromagnetic clutch comprising a driving member of paramagneticmaterial, said member having an internal space, an energizing windingmounted in said space, slip ring and brush means operatively associatedwith said member for connecting said winding to an external currentsource, said member comprising a substantially cylindrical inner partand an annular outer part, said inner part having a radially outwardlyextending pole piece including a face disposed substantially axially ofsaid member, said outer part having a radially inwardly extending polepiece including a face disposed substantially parallel to said firstface and defining therewith a magnetic gap, a driven member having aparamagnetic part positioned in said gap to define with said faces apair of annular spaces, a casing carried by said driving memher andenclosing said driven member, and a mass of pulverulent paramagneticmaterial disposed in said casing the bulk of which material is adapted,upon energization of the clutch, to be positioned in said spaces tounite said driving and driven members for joint rotation, a nonmagneticelement in contact with said pole pieces on that side thereof oppositesaid driven member and bridging said gap, to confine said material tosaid spaces, a second non-rnagnetic annular element juxtaposed to theouter face of said inwardly extending pole piece, and said driven memberbeing provided with a non-magnetic part both said element and part beingdisposed contiguous to said gap.

References Cited in the file of this patent UNITED STATES PATENTS2,315,298 Thompson Mar. 30, 1943 2,488,079 DeLavaud et al Nov. 15, 19492,488,827 Pensabene Nov. 22, 1949 2,519,449 Findley Aug. 22, 19502,525,571 Winther Oct. 10, 1950 2,573,065 Salemme Oct. 30, 19512,575,360 Rabinow Nov. 20, 1951 OTHER REFERENCES Magnetic Fluid Clutchin Servo Applications, Electronics, November 1949, pages -103.

The Magnetic Fluid Clutch, AIEE Transactions, vol. 67, printed December13, 1948.

Contributed Original Research, Journal of Applied Physics, vol. 20,December 1949, pages 1137-1140.

1. AN ELECTROMAGNETIC CLUTCH COMPRISING A ROTATABLE DRIVING MEMBERINCLUDING A PAIR OF ANNULAR POLES SO DISPOSED AS TO DEFINE AN ANNULARGAP, ELECTRICAL MEANS CARRIED BY SAID MEMBER FOR PROVIDING MAGNETIC FLUXIN SAID GAP UPON ENERGIZATION OF THE CLUTCH, A ROTATABLE DRIVEN MEMBERINCLUDING A PARAMAGNETIC ANNULAR PART POSITIONED IN SAID GAP ANDDEFINING AN OUTER ANNULAR GAP AND AN INNER GAP, A CASING CARRIED BY SAIDDRIVING MEMBER FOR ENCLOSING SAID GAP AND DRIVEN MEMBER, A MASS OFPULVERULENT PARAMAGNETIC MATERIAL DISPOSED IN SAID CASING THE BULK OFWHICH MATERIAL IS ADAPTED UPON ENGERGIZATION OF THE CLUTCH TO TAKE UP APOSITION IN SAID GAPS FOR UNITING SAID PART AND DRIVING MEMBER FOR JOINTROTATION, A NON-MAGNETIC ANNULAR ELEMENT UNITED WITH SAID DRIVING MEMBERAND POSITIONED ON ONE SIDE OF SAID OUTER GAP, A SECOND NON-MAGNETICANNULAR ELEMENT UNITED WITH SAID DRIVING MEMBER AND POSITIONED ON THEOPPOSITE SIDE OF SAID OUTER GAP AND BRIDGING ACROSS BOTH SAID GAPS, ANDA NON-MAGNETIC ANNULAR ELEMENT UNITED WITH SAID DRIVEN MEMBER APOSITIONED ADJACENT SAID INNER GAP ON THE SAME SIDE THEREOF AS SAIDDRIVEN MEMBER.